Numerical analysis of the heat and mass transfer process in absorbers using water and lithium bromide

Abstract

This study aimed to simulate the heat and mass transfer process of a spiral tubular Lithium Bromide/Water (LiBr/H2O) absorber based on a non-linear mathematical model developed in MATLAB program, using an iterative numerical method and experimental data from the literature for calibration and validation. For this, the absorber was simplified as a descending film flat plate and the simulation considered three different cases of cooling water temperature variation: 21.5°C, 23.5°C, 25.6°C. The effective mass transfer coefficient, Kef, was obtained from the literature, and the overall heat transfer coefficient, U, was calculated using the overall thermal resistance within the absorber. The distributions for the temperature and concentration of the solution and cooling water, obtained by the model, showed good agreement when compared to the literature. It was found that the heat and mass transfer increased when varying the absorber length up to 14.25 m, and from this value on, they remained nearly constant. Increasing the mass flow rate of the cooling water inlet decreases the temperature and concentration of the LiBr/H2O. In addition, copper and aluminum proved to be more suitable for use in the absorber tube than stainless steel.